Hi Piotr,
Exactly the same thing has happened to me (Safair/Mac), but I just assumed it was because I'm travelling, and not on my normal network. Maybe not though? I'll know when I get home on Wednesday.
Malcolm

Piotr, it must be your IE.
Here I can see read/unread messages correctly on Safari (Mac) and simultanuously in IE (Win, same machine thanks to Virtual Machine/Parallels).

Best P.

Something must be going on - not only do visited threads still display in bold fonts, but I never see new posts when inside a thread, until I refresh the page...

Of course, I tried my IE setting, and the reload setting is at "Auto" (as before); I tried the "Refresh pages each time" option but it doesn't change anything. And, it only behaves that way with DVINFO board.

Yes I get these issues too and some of the ones Chris Soucy posted about.

Chris (Hurd) did post on Friday that they were working on resolving all the recent board issues like this but that it could take a bit of time - whilst they digest all that Thanksgiving holiday turkey no doubt! I'm sure it'll all be resolved in a few days. My pet theory is that it's the 1000 plus SXS alternatives thread in the XDCAM EX1/3 section that's screwed it all up! (joke!)

After I read a thread, it no longer appears in the 'new posts' list--I read this, 'new posts', not there--had to go to the individual forum to post this response. Refreshing does not seem to help.

Also, can the 'new posts' become old posts time be increased? Sometimes I'll follow an external link and by the time I'm finished, I have 'no' new posts. I see that the forum is keeping track of old posts that haven't been read--is that supposed to achieve the same thing?

Seems there is a cache feature activated on the server that is not serving the latest version of a page. A refresh is needed to see the new posts.
I changed nothing for month in my PC and this problem occurs only since few days and on several PC, so it is definitely server side.
is it because the "The threads below have not been updated since your last visit but still contain unread posts." feature ? I cannot remember having seen that before on DVinfo (these Vbulletin looks all the same)

Once you hit a thread, unless someone posts something else in that thread the thread will be marked as read for you. If you don't read a thread for 10 days after the last post, it'll be marked as read.

The server isn't caching any pages, but you may still have some cached pages on your local machine from before I updated the expiration time. (Or, if you have some kind of web proxy infront of you it may be caching them.) A reload on those pages should clear that, though.